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'Unhackable' quantum broadband step closer after breakthrough by Chinese scientists

PUBLISHED : Thursday, 09 April, 2015, 8:00am
UPDATED : Friday, 17 April, 2015, 6:43pm

A breakthrough by Chinese scientists has brought high-speed, quantum broadband communication a step closer.

Scientists at the University of Science and Technology in Hefei, Anhui province, have demonstrated for the first time that quantum information can be stored and distributed using a broadband communication protocol.

Writing in the British journal Nature Photonics the researchers said the technology showed "great promise for the establishment of quantum networks in high-speed communications".

Unlike traditional communication methods, quantum broadband would be immune to hacking, the researchers said.

Anyone who tried to detect or measure the quantum bits - entangled photons that carry information in various quantum states - would destroy the information, rendering it impossible to read and alerting the recipient.

The "unhackable" nature of quantum broadband is the primary reason the Chinese government is investing in quantum communication. The world's longest quantum network and first quantum communication satellite are both being built in China.

Current quantum networks are plagued by narrow bandwidth and slow speeds, mainly due to the difficulty of maintaining fragile quantum states over long distances.

They are only able to distribute short key chains used to encrypt data transmitted on conventional networks, an improvement in security but not the dramatic step envisaged by the scientists.

Professor Shi Baosen, one of the authors of the paper, said that his team's work was partly the result of intense international competition.

Many countries are racing to develop the world's first quantum communication "expressway", said Shi.

A team in the UK had tried to add "fuel" to travelling qubits - the basic unit of information in a quantum computer - but increased speed had led to increased instability and more "accidents".

Shi's team took a different approach. In addition to building "fuel stations", they also imposed restrictions to regulate the movement of qubits and slow them down when necessary.

To achieve this they used lasers to freeze fast-moving photons and developed new methods to control the network flow.

"Our cold approach is more sophisticated and required bulkier equipment to set up, but it produced better results, which helped us win the race," Shi said.

The new technology would be useful not only in quantum communication, but also in the construction of quantum computers. In theory, it could allow entangled photons to run around a fibre loop with an optical switch that would release them whenever they were needed, thus providing a "memory chip" for quantum computers.

But Shi said that lots of work remained to be done before the first quantum broadband network could be built.

For instance, the laboratory setup was still too large, too sophisticated and too costly for mass application.